Current regulating system



Nov. 15, 1955 J. H. LINDBERG CURRENT REGULATING SYSTEM Filed May 7, 1952INVENTOR JOHN HELGE LINDBERG BY HIS ATTORNEYS United States PatentOCURRENT REGULATING SYSTEM Iohn Helge Lindberg,,Sundbyberg, Sweden,assignor to A B Svenska Flaklfabriken, Stockholm, Sweden, a corporationof Sweden Application May 7, 1952, Serial No. 286,649 Claims priority,application SwedenMay 11, 1951 6 Claims. (Cl. 323-7 The presentinvention relates to a control system for stabilizing the operation ofelectrofilters which are supplied from a source by means of a highvoltage transformer.

A primary object of the present invention is to eliminate releases inthe operation of the electrofilter which are occasioned by sudden risesof current, for example, when changing the operation of the filter.

A further object of the present invention is to provide a control systemwhich obviates the necessity for manual control of the voltage of anelectrofilter. 1

These and other objects of the present invention and the variousfeatures and operation thereof are more fully set forth hereinafter withreference to the accompanying drawing, in which, l

The figure is a schematicv wiring diagram of a protective circuit forthe power supply of an electrofilter.

The invention contemplates a control system wherein a given number ofseries resistances are connected into the primary circuit of the highvoltage transformer of the electrofilter. The number of resistancescorresponds to the number of regulating steps desired to preventexcessive current in the electrofilter. For each resistor, a currentresponsive relay is connected in series in the primary circuit to effectinsertion or removal of the resistances from the circuit.

Referring now to the drawing, a control circuit having terminals 1 and11 is inserted in one side of the primary circuit of a high voltagetransformer, the other side being indicated at 50. The transformersupplies power to an electrofilter. The terminals 1 and 11 are connectedthrough a pair of resistances 2 and 3 in series with a fixed resistance4 and a pair of current responsive relays 6 and 10, respectively. Eachrelay controls a resistance; for example, the relay 6 controls theresistance 2 and the relay controls the resistance 3.

The relays 6 and 10 are connected in the control circuit in similarmanner and in order to facilitate a description thereof only theconnections affecting the relay 6 and the operation thereof will bedescribed in detail.

The relay 6 controls a pair of contacts 7 and 8 by means of a switch arm6a responsive to the current in the coil 5 of the relay. The contacts 7and 8 are normally open but are adapted to be closed when the currentthrough the relay coil 5 exceeds a predetermined maximum value andactuates the switch arm 6a from the rest contacts 7' and 8' to theworking contacts 7 and 8. The contacts 7 and 8 are connected in serieswith the relay coil of a second relay 24 so that when the relay 6 isenergized the second relay 24 will also be energized. The circuit forthis runs from the upper side of an auxiliary source M through thejunctions 16 and 15, the contacts 8 and 7, the junction 26, the relaycoil 25, and back to the other side of the source M. The relay 24 isprovided with a pair of normally closed contacts 27 and 28 which areadapted to be open when the relay is energized, for example, when thecurrent through the relay 6 exceeds the predetermined maximum value.

The contacts 27 and 28 control the insertion and removal of theresistance 2 from the primary circuit. When the switch arm 29 is in itsnormal position against the rest contacts 27 and 28, the resistance 2will be shunted out of the primary circuit by means of the shunt circuitrunning from the left hand end of the resistance through the junction30, the contacts 27 and 28, the junctions'23 and 31 and back to theright hand side of the resistance 2. Thus, when the relay 24 isdeenergized, the resistance 2 Will be shunted out of the circuit and thecurrent through the primary circuit will be at a maximum. Should thecurrent rise above the desired level, the relay 6 will be energizedwhich in turn will energize the relay 24 to open the shunt circuit ofthe relay 2 by raising the arm 29 against the contacts 27' and 28.Opening the shunt circuit causes the current in the primary circuit topass through the resistance 2, increasing the resistance in the circuit,and thereby reducing the current.

Means is provided to prevent deenergization of the relay 24 when thecurrent through the primary circuit is reduced to a safe value. In thepresent instance, the means comprises a holding circuit for the coil25which is controlled by a voltage responsive relay 33. The voltageresponsive relay 33hasits coil 32 connected across the resistance 2 asindicated at the junctions 30 and 37, 31. Thus, when the resistor isshunted out, as when the relay 24 is deenergized, there is no voltagedrop across the resistor and the relay 33 is deenergized so that its arm36 lies against the rest contacts 34 and 35'. When the shunt circuit forthe resistor 2 is broken, however, the current; flowing through theresistor 2 effects a voltage drop between the points 30 and 31, whichenergizes .the relay 33. The relay 33 has a pair of normally openworking contacts 34, 35 which are operable to provide an alternativecircuit for energizing the relay coil 25. of the relay 24. Thisalternative circuit runs from the source M through the junctions 16 and43, the contacts 35 and 34, the junction 26, the coil 25, and back tothe other side of the source M. In this manner, as soon as the shuntcircuit for the resistor 2 is broken, the relay 33 is energized to holdthe relay 24 open until the voltage drop across the resistor 2 fallsbelow a predetermined minimum value. When this occurs, the relay 33 isdeenergized, and the arm 36 falls against the resting contacts 34' and35', opening the circuit through the contacts 35 and 34, deenergizingthe relay 24, and closing the shunt circuit for the resistor 2. Theresistor 2 is then shunted out of the primary circuit which causes thecurrent to rise again to the desired level.

Other means may be provided to present deenergization of the coil 24when the shunt circuit for the resistor 2 is broken initially. Forexample, the current relay 6 may be provided with a series resistancewhich is operable to be disconnected after actuation of the currentrelay. In another modification, the current relay 24 may be providedwith two counteracting windings, one of which is connected only uponactuation of the relay. As an additional modification, the current relaymay he possessed of a relatively high energization current and a lowerdeenergization current. In each of these modifications, the relay 33 andits associated circuits may be eliminated from the system and modifiedcurrent coil will replace the current coil 6.

The second resistor 3 and its associated relay 10 provide a furtherregulation of the current through the primary circuit. If when the relay24 is energized to insert the resistance 2 the current rises above asafe value, the resistance 3 will be inserted in the circuit by breakingits shunt circuit through the contacts 20' and 21. The components of thecircuit for controlling this shunt circuit comprise the currentresponsive relay 10 having a coil 9 and a switch arm 14 operable betweenthe contacts 12, 13' and 12, 13, a second relay 18 having a coil 17 andan arm 22 operable between the contacts 20', 21' and 20, 21, and avoltage-responsive relay 39 having a coil 38 and a switch arm 42operable between the contacts 40, 41 and 40, 41. The relays 10, 18 and39 operate like the relays 6, 24-, and 33 respectively to control theshunt circuit for the resistor 3 and thereby the current in the primarycircuit.

If the possible current variation in the primary circuit is greater thanthat that can be compensated for by the two resistances 2 and 3, agreater number of resistances may be added to provide the desired amountof regulation. Each of the additional resistors will be controlled by acurrent responsive relay similar to the relays 6 and 10.

While the particular embodiments have been illustrated and describedherein, it is not intended to limit the invention to such description,but changes may be made therein and thereto within the scope of thefollowing claims.

What I claim is:

1. In a power supply for a primary coil, a primary circuit comprising atleast one resistor and a currentresponsive relay both in series withsaid primary coil, said relay having normally open contacts operable tobe closed when the current through said primary circuit exceeds apredetermined minimum value, a second relay connected to a sourcethrough said normally open contacts and having normally closed contactsoperable to be opened when the second relay is energized, ashort-circuit shunt for the resistor through said normally closedcontacts, the latter contacts, upon energization of said-second relay,opening said shunt and reducing the current through said primarycircuit, and means rendered operative upon energization of said secondrelay to maintain said shunt circuit open until the current through theprimary circuit falls below a predetermined minimum value.

2. A power supply according to claim 1 wherein said last-mentioned meanscomprises a voltage responsive relay connected in parallel with saidnormally closed contacts and operable to be energized when the lattercontacts are open and the current through said resistor in the primarycircuit exceeds said predetermined minimum value, said voltageresponsive relay having normally open contacts operable when closed tocomplete a holding'circuit operable to retain said-second relayenergized.

3. A power supply according to claim 1 wherein said current-responsiverelay includes a series resistance operable to be disconnected from saidrelay upon actuation thereof to constitute said last-mentioned means.

4. A power supply according to claim 1 wherein said current-responsiverelay comprises two counteracting windings, one of which is operable tobe disconnected upon actuation of said current-responsive relay toconstitute said last-mentioned means.

5. A power supply according to claim 1 wherein said current-responsiverelay is operable to be de-energized only when the current therethroughfalls below said predetermined minimum value to constitute saidlast-mentioned means.

6. In a power supply for a primary coil, a primary circuit comprising aplurality of current-responsive relays and a resistor for each saidrelay all in series with said primary coil, each said relay havingnormally open contacts operable to be closed when the current throughsaid primary circuit exceeds a predetermined maximum value, a pluralityof second relays, each connected to a source through said normally opencontacts of one of said current-responsive relays and having normallyclosed contacts operable to be opened when the second relay isenergized, a short-circuit shunt for each resistor through said normallyclosed contacts of one of said second relays, the latter contacts uponenergization of said second relay, opening said shunt and reducing thecurrent through said primary circuit, and means rendered operative uponenergization of said second relay to maintain said shunt circuit openuntil current through the primary circuit falls below a predeterminedminimum value.

References Cited in the file of this patent UNITED STATES PATENTS

